On a busy street in one of the most affluent areas of London, a handful of committed demonstrators are conducting a 24-hour picket of a large building complex. The activists bear home-made banners with slogans such as “Ukraine is on fire”, and wave the country’s blue-and-yellow flags at the development in Knightsbridge.

The target of their demonstration, however, is not one of the tottering regime’s outposts in the city. The Ukrainian embassy is a couple of miles away in Holland Park, while Ukreximbank, the state import-and-export bank, has offices in the City.

Instead the protest is, perhaps surprisingly, targeted at an ostensibly private individual: Ukraine’s wealthiest man, Rinat Akhmetov, who lives at One Hyde Park in the most expensive flat in Britain.

Mr Akhmetov, who paid £136 million for the three-storey penthouse in 2011, is one of several oligarchs with businesses and property in London whose assets, the campaigners believe, should be frozen in order to force them to intervene in Ukraine’s political crisis.

“The richest man in Ukraine should be responsible for the people he has got an influence on,” says Andriy Aleksyeyev, a 43-year-old graphic designer.

Mr Aleksyeyev was among the dozens of Ukrainian activists who rushed to the building on Thursday when word spread that Mr Akhmetov’s private jet had been spotted landing at Farnborough, Hants. As it turned out, he was not on the aircraft, choosing instead to remain in Ukraine. The vigil, however, is being maintained to ensure that he does get the message when he returns.

It might appear odd that a businessman, whose holdings include an energy company and a steel firm, should be held responsible for any part of the clashes between demonstrators and government forces in Kiev that have left scores dead. But it is said that Mr Akhmetov’s political friendships give him a great deal of clout.

The 47-year-old controls nearly half of Ukraine’s coal, steel and thermoelectricity sectors, and is known to have influence over a bloc of up to 40 of the country’s MPs. In December, he lent the president, Viktor Yanukovych, his jet to fly to Moscow when the leader’s official aircraft was undergoing maintenance. The move prompted a demonstration outside One Hyde Park that would foreshadow the return of demonstrators to the building last week.

A second oligarch singled out by protesters is Dmitry Firtash, a gas magnate. His links to the Ukrainian regime were highlighted when he opened a day of trading at the London Stock Exchange last year as part of a charity festival under Mr Yanukovych’s patronage.

The protest outside One Hyde Park came as the European Union agreed to impose travel bans and asset freezes on Ukrainian officials deemed responsible for the violence. The move – which, following the effective ousting of Mr Yanukovych, now appears to be in flux – was seen by some as a “shot across the bows” of wealthy businessmen with assets in London who were considered to be tacitly supporting attacks on demonstrators by failing to intervene. The call for the sanctions to cover oligarchs who do not hold current political office was also backed by some policy experts and economists.

Damon Wilson, a former White House official involved in US sanctions against Ukraine in 2004, was in favour of such a move, saying it would force influential businessmen to act, rather than simply being “punitive”.

Both Mr Akhmetov and Mr Firtash have released recent statements that distance themselves from the government’s actions, and Mr Akhmatov has told friends that he has been “working tirelessly” behind the scenes with key figures involved in resolving the dispute.

However, imposing sanctions would force them either to entirely “opt out” of their association with the regime or “defect outright”, Mr Wilson said.

“Fundamentally, what you want to do is convince important actors like this that for them to thrive, they themselves need to make the transition to being credible, legitimate business actors in the West. When you raise the personal cost of their association with these degrees of actions, they need to think about where they are going to be sitting when the music stops.”

Economists say the potential impact of freezing the assets that wealthy Ukrainians hold in Britain should not be underestimated.

“It would essentially take them out of business in Europe,” says Anders Aslund, a Swedish economist and senior fellow at the Peterson Institute for International Economics.

Whereas before the financial crisis Ukrainians favoured Cyprus as a centre for their commercial operations, “today London is the financial centre of Ukrainian businessmen”.

The identities of the individuals the EU’s sanctions were intended to affect have not yet been disclosed. Before Mr Yanukovych’s virtual removal, diplomats were expected to draw up a list of names imminently, and the threat still hangs over Mr Yanukovych.

It is possible that it was intended to include the president’s family, including his son, Oleksandr, whose business empire is valued at £306 million – a move that was supported by those who want to exert the greatest possible pressure on the regime.

There is “no doubt” that many of the country’s oligarchs will have “big money” banked in Britain, according to Mr Aslund. Although it is unclear what assets Oleksandr might have in the UK, it would be “very strange” if he did not have “substantial” funds in the country, he added.

Observers point out that the oligarchs with bases in London are by no means a homogeneous group, and the seizure of much of Ukraine's political system by protesters on Saturday will also cast doubt on how much influence each will retain in the coming months.

Policy experts said that any freezing of assets should not affect those who had clearly attempted to break away from Mr Yanukovych since the country’s “turn to repression”.

Among those considered to be in this more favourable category is Viktor Pinchuk, a steel magnate and philanthropist worth about £2.7 billion. Mr Pinchuk, 52, made his fortune after marrying the daughter of Leonid Kuchma, Ukraine’s former president, and is a donor to Tony Blair’s Faith Foundation.

However, any restrictions imposed on wealth would make any of the oligarchs highly nervous. Mr Akhmetov, for instance, is worth about £9 billion, making him the richest man in Ukraine. He has substantial assets in Britain and his wife Liliya is understood to have a particular fondness for London.

His main holdings company, System Capital Management, opened offices in Park Lane in 2012 and Metinvest, a steel producer in which Mr Akhmetov’s firm is the majority shareholder, has a plant in Newcastle. SCM’s website describes its London office as the “logical next step” as the company seeks to “promote our business to the international business community”.

Mr Firtash, 48, whose fortune the Ukrainian Forbes put at £600 million in 2011, owns gas and chemical firms through his holding company, Group DF. His wife Lada is founder of the couple’s UK Firtash Foundation, which organised a “Days of Ukraine” celebration in Britain last year, sponsored by Mr Firtash’s firm.

To mark the three-day festival last October – before violence erupted in the country – the couple enjoyed their high-profile engagement at the London Stock Exchange. On the festival’s website remains a proud declaration that the initiative “enjoys the patronage of the President of Ukraine” – an endorsement that might now have lost its sheen.

Months later, a protest aimed at Mr Firtash and held outside the building as people died from gunshot wounds after clashes with police about 1,500 miles away, made clear that activists felt responsibility for the violence now fell partly on him. Their sentiments were summed up by one of the posters, which read: “London doesn’t want your bloody money."